|Events during December
The Moon: Full – 5th, Last quarter – 12th, New moon – 20th, First quarter – 27th and close to Spica (see snapshot 1) on the 15th. Saturn
is stationary on the 6th, the Geminids meteor shower is from the 12th to 14th with favourable viewing conditions, and the winter solstice, when the Sun
reaches its most southerly point over the Tropic of Capricorn, is on the 22nd.
SE Dawn Sky 13/12/2006
In the above snapshot, Jupiter, Mars and Mercury are rising close together in the southeast dawn sky during early December. On the 7th
Mercury will be above Mars, and Mars above Jupiter. On the 10th the three planets will form a circle about twice the Moon`s diameter and, by the 13th
Jupiter is above Mars and Mars above Mercury. They should all be easily seen by eye and through binoculars, with Jupiter the brightest at –1.7 magnitude,
Mercury at –0.6 and Mars at 1.5. It is very unusual to have three planets so close together.
The deep sky objects within the region of the sky shown on the snapshot are:
M5 – a globular cluster in the constellation of Serpens, 23 light years away. At 5.6 magnitude, under good conditions this can be
observed with the naked eye. Through good binoculars it is seen as a small fuzzy patch and through a 3” telescope as a round nebula brighter towards the
centre. With a 4” telescope upwards the brightest stars can be resolved, whilst large telescopes reveal thousands of stars.
M10 – a globular cluster in Ophiuchus at 7.5 magnitude and 13 light years away.
M12 – another globular cluster in Ophiuchus at 8.0 magnitude and 18 light years.
M83 (the Southern Spinwheel) - a spiral galaxy in Hydra at 8.5 magnitude and 10,000 light years.
M104 (the Sombrero Galaxy) – a spiral galaxy in Virgo at 9.5 magnitude and 50,000 light years, with a wheel of dust and a halo of stars.
The other objects shown are:
Arcturus – the brightest star in the constellation of Bootes and, with a magnitude of –0.04, the third brightest in the night sky after
Sirius and Canopus. Arcturus is a red giant with 110 times the luminosity of the Sun. It is thought to be 36.7 light years from Earth.
Spica – the brightest star in the constellation of Virgo with a magnitude varying between 0.92 and 1.04. Spica lies close to the
ecliptic (the apparent path of the Sun and planets across the sky) and can be eclipsed by the Moon and (rarely) by the planets. One way to find Spica is to
follow the arc of the Plough´s handle to Arcturus (see Constellations) and continue the same distance again.
SW Dusk Sky 25/12/2006
The second snapshot shows Venus about to set low in the southwest after sunset on Christmas day. Neptune will set an hour and a half
later and Uranus, following the Moon, after a further hour and a half.
The Deep Sky objects shown are:
M2 – a globular cluster in Aquarius at 7.5 magnitude and 36 light years.
M11 (the Wild Duck Cluster) – an open cluster in Scutum at 6.3 magnitude and 6 light years.
M15 (the Pegasus Cluster) – a globular cluster in Pegasus at 6.2 magnitude and 33 light years.
M27 (the Dumbbell Nebula) – a planetary nebula in Vulpecula at 7.4 magnitude and 1.25 light years.
Also shown is Altair, the brightest star in the constellation of Aquila which, at 0.77 magnitude, is easily visible in the night sky.
||Mercury is at –0.6 magnitude during the first two weeks of December, visible low in the southeast. It is very
close to Mars and Jupiter during the second week.
The best times to observe Mercury are when it is an evening star in the spring and a morning star in the autumn. In midsummer the lighter skies make visibility difficult near the horizon.
||Venus is visible low in the southwest after sunset during late December.
On the 8th June 2004, Venus was at inferior conjunction
and transited the sun. Transits of Venus are rare, taking place at greater
than 100 year intervals and usually in pairs. The last two transits of Venus were in 1874 and 1882. June's transit
began at 7.20h and lasted 6 hours until 13.20h, the total event visible from Europe as a small black disc crossing
the lower part of the sun from left to right. The next transit will be in late June 2012. After that, transits of Venus
won't occur again until 2117 and 2125.
Before and after inferior conjuction, when Venus is
the closest it comes to the earth, are the times at which the planet is most brilliant and can be seen setting or rising
4 hours after or before the sun. The dates of the next two inferior conjunctions are October 28th 2010 and October 26th 2018.
||Mars is at 1.5 magnitude low in the southeast morning twilight, moving from Libra to Scorpio. The Moon is
closeby on the 19th.
At opposition on the 28th August 2003, Mars was only 56 million kilometres from the earth. It showed a
disc of 25.1 seconds of arc across which is almost as large as it can ever appear. Mars started 2003 at 310 million kilometres from
the earth at 4.5 seconds of arc and 1.6 magnitude. By opposition it brightened 50 times to reach -2.9 magnitude but faded to 0
magnitude by December. Even to the naked eye Mars was a striking object in the summer and autumn sky, easily identifiable by its
reddish hue in an area of sky poor in bright stars. Mars will not be as close again for another 15 years.
These favourable oppositions occur every 15 years but other oppositions occur at average intervals of 2 years 2 months. In general Mars is observable every other year, being too close to the sun for favourable conditions during other times. Brightness at opposition varies from -1.0 to -2.9 magnitude, and when furthest from the earth it fades to 1.7 magnitude. The planet can be identified by its orange-red colour.
||Jupiter is at –1.7 magnitude, moving from Libra through Scorpio into Ophiuchus and into a dark sky by the end
of December. The Moon is closeby on the 19th.
Being 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than with Mars, from about -2.8 to -1.8 magnitude.
The 4 largest moons of Jupiter are easily visible through a small telescope, ranging from 4.6 to 5.6 in magnitude. The innermost, Io, takes 1.8 days to orbit the planet making its motion easily detectable within a few minutes.
||Saturn is at 0.3 magnitude in Leo and rises before 21.00h by the end of the month. It is stationary on the 6th
with the Moon closeby on the 9th.
Saturn crossed the equator into the northern hemisphere in 1996 where it will remain until 2010 with the southern side of the ring system facing the earth. Because of its distance, its brightness varies little between opposition and conjunction but is affected by the huge ring system. Seen edge on the rings contribute little or no light.
Every 15 years the plane of Saturn's rings passes through the sun, illuminating first the north and then the south side. For a few days the rings are edge on to the sun. About the same time the earth passes through the ring plane and, depending on the earth's position this may happen just once or 3 times. During 1995/96 there was a triple crossing and the next will be 2038/39. The next single crossings will be in 2009 and 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
||Uranus in Aquarius sets about 22.30h by the end of December. The Moon is closeby on the 25th.
Brightness varies slightly reaching 5.6 magnitude at opposition. This is bright enough to see with the naked eye but identifying it against the stars is difficult.
||Neptune remains in Capricorn and sets about 20.00h by the end of the month. The Moon is closeby on the 23rd.
Neptune has an average magnitude of 7.9 which varies little with changing distance.
||Never brighter than 13 magnitude, Pluto is only visible through powerful telescopes and we will therefore not be reporting on its position in the sky.|
||Full moon: 5th
Last quarter: 12th
New moon: 20th
First quarter: 27th